I tried out the Trinity Desktop Project this weekend on Debian Lenny. Trinity is an attempt to continue development and bugfixes on KDE3 for distributions that are moving to KDE4. I would not recommend it on Lenny. It didn't make a DM entry for the old KDE, it preserved but did not import user settings. Kmail kept crashing, and I could not run the old kmail remotely over ssh. On removing all the trinity packages (aptitude purge ~ntrinity), kdm had problems determining what session to start. Fortunately, I was able to go through it's session menu and get back to the old KDE.